The example “Who’s Looking v2 JIRA Connect add-on” has descriptor atlassian-connect.json and property version. However, the version property is not described in https://developer.atlassian.com/cloud/jira/platform/connect-app-descriptor/ I have just found it’s description in the schema https://bitbucket.org/atlassian/connect-schemas/raw/master/jira-global-schema.json that:
This field is reserved for Atlassian Marketplace. Any value provided will be ignored …
So, I think the “Who’s Looking v2 JIRA Connect add-on” should omit version in atlassian-connect.json and it would be nice to document this on the https://developer.atlassian.com/cloud/jira/platform/connect-app-descriptor/